[glorfindel]

You make a good point. I'm not sure poker follows a normal distribution either. Most of the stuff I've found so far assumes it, but that certainly doesn't mean it's correct.

My background before poker was card counting in blackjack and the acknowledged mathematics guru in blackjack, Don Schlesinger ("Blackjack Attack"), used a normal distribution for his calculations involving standard deviation. Now, while it's true your win/loss range per hand of blackjack is not as large as poker, it still varies substantially. For instance, you may place 1 bet, split 3 times, double on each split and end up losing or winning 8 bets.

In your example of the coin toss, your expectation over 10 trials would be $5 but it's entirely possible you would win $0 or $20. Standard deviation will answer "what is the probability I will win $0 or win 20$ over 10 tosses." That seems consistent with poker.

I think your concern may be with the "15BB/100" as the assumed limit hold'em standard deviation. I don't know how this number was derived, but I will try to find out.